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Effects of Biologically Active Metabolites of Tamoxifen on the Proliferation Kinetics of MCF-7 Human Breast Cancer Cells in Vitro

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Effects of Biologically Active Metabolites of Tamoxifen on the Proliferation Kinetics of MCF-7 Human Breast Cancer Cells in Vitro [CANCER RESEARCH 43, 4618-4624, October 1983] Effects of Biologically Active Metabolites of Tamoxifen on the Proliferation Kinetics of MCF-7 Human Breast Cancer Cells in Vitro Roger R. Reddel, Leigh C. Murphy, and Robert L. Sutherland1 Ludwig Institute for Cancer Research (Sydney Branch), University of Sydney, Sydney, New South Wales 2006, Australia ABSTRACT tumor tissues of patients treated with tamoxifen is DMT, with 4OHT being present at much lower concentrations (1, 7,13, 25). The effects of two major metabolites of tamoxifen, /V-de- Prompted no doubt in part by the early misidentification of the methyltamoxifen (DMT) and 4-hydroxytamoxifen (4OHT), on major metabolite as 4OHT, there has been considerable interest MCF-7 Å“il proliferation and cell cycle kinetic parameters were in the antiestrogenic and antitumor activity of 4OHT (2, 3, 6,15, compared with those of the parent compound. All three com 16, 33). In contrast, there have been very few studies on the pounds produced dose-dependent decreases in the rate of cell biological activity of DMT (6, 33). proliferation which were accompanied by decreases in the per In the present study, we have attempted to answer the follow centage of S- and G2-M-phase cells. 4OHT was 100- to 167-fold ing questions. Do the metabolites DMT and 40HT differ from more potent than both tamoxifen and DMT in producing these tamoxifen in their actions on the proliferation and cell cycle effects, and this was correlated with their relative binding affini kinetics of human breast cancer cells? What are the relative ties (RBAs) for the cytoplasmic estrogen receptor (ER) (17/3- potencies of these 3 compounds in their actions on such cells in estradiol = 100, 4OHT = 41, tamoxifen = DMT = 2). At doses vitro? What therefore is the likely contribution of each to the <2.5 ¿IM,theseeffects were completely reversed by 170-estra- antitumor activity observed in vivo? Can the relative potencies diol, but the required 170-estradiol:antiestrogen concentration of these compounds in producing these effects be related to ratios differed, i.e., 1:10 to 1:1 for 4OHT compared with 1:1000 their RBAs for the ER or the more recently described high-affinity to 1:100 for tamoxifen and DMT. Although the concentrations of antiestrogen binding site (23, 30)? 170-estradiol required for reversal were related to affinity of the It has previously been shown in this laboratory that tamoxifen metabolite for ER, they were 5- to 20-fold lower than predicted has growth-inhibitory effects on the MCF-7 human breast cancer from the measured RBAs. When the rate of cell proliferation was cell line and that not all of these effects are reversed by simul measured over a range of concentrations of antiestrogen, in the taneous treatment with 17/3-estradiol (27, 28). These inhibitory presence or absence of 17/î-estradiol,it was highly correlated effects were shown to be accompanied by accumulation of cells (r2 = 0.96) with the percentage of S-phase cells. In addition to in the GO-G! phase of the cell cycle (27, 28), due mainly to an these 17/3-estradiol-reversible events, all three compounds increase in the proportion of "slowly cycling" cells (28, 32). The caused 17j8-estradiol-irreversible cytotoxicity at higher concen MCF-7 cell line forms a particularly suitable experimental model trations (>7.5 U.MDMT and 4OHT, 10 MMtamoxifen). The order to compare the effects of tamoxifen and its metabolites since it of potency in producing this effect was DMT > 4OHT > tamox has previously been shown that metabolism of tamoxifen is ifen, which correlated with neither the RBAs for ER nor the RBAs negligible in these cells in vitro (3,14). for the high-affinity microsomal antiestrogen binding site. These data support the concept that estrogens and antiestro- MATERIALS AND METHODS gens compete for a common event which regulates the rate of cell proliferation probably by controlling the proportion of cells Cells. MCF-7 cells (26) in their 299th passage were supplied by Dr. entering S phase. Although it appears likely that ER is intimately Charles M. McGrath, Meyer L. Prentis Cancer Center, Detroit, Mich., involved in this regulatory process, 17ß-estradiol-irreversible and maintained as described previously (28). Stock cells were passaged weekly with an inoculation density of 3 x 106 cells/150-sq cm flask into mechanisms are also involved in antiestrogen action in vitro. 50 ml Roswell Park Memorial Institute Medium 1640 supplemented with 20 mw 4-(2-hydroxyethyl)-1-piperazineethanesulfonicacid buffer, 14 mM INTRODUCTION sodium bicarbonate, 5 mw L-glutamine, gentamicin (20 ¿tg/ml),insulin (10 Mg/ml), and 10% fetal calf serum. Tamoxifen, a nonsteroidal antiestrogenic compound, has been Drug Treatment. Tamoxifen [frans-1-(4-/3-dimethylaminoethoxy- widely used in the treatment of human breast cancer on account phenylM ,2-diphenylbut-1-ene], N-demethyltamoxifen [frans-1-(4-,8-meth- of its efficacy and relatively low toxicity (22). Although this agent ylaminoethoxyphenyl)-1,2-diphenylbut-1-ene], and 4-hydroxytamoxifen has been in clinical use for over a decade, the mechanism of its [frans-1-(4-0-dimethylaminoethoxyphenyl)-1-(4-hydroxyphenyl)-2-phen- action remains incompletely understood (29). ylbut-1-ene] were supplied by I. C. I., Ltd., Pharmaceuticals Division, The original studies of tamoxifen metabolism identified 4OHT2 Macclesfield, Cheshire, United Kingdom. Stock solutions (10 mw) were prepared in analytical grade ethanol and stored at -20°. These drugs as the major metabolite (11, 12), but more recently it has been shown that the major metabolite accumulating in the plasma and were added to culture medium as described previously for tamoxifen (28). 17/3-Estradiol was acquired and handled as described previously (28). 1To whom requests for reprints should be addressed. Growth Curves. Exponentially growing cells (5 x 104) from Day 5 2 The abbreviations used are: 40HT, 4-hydroxytamoxifen; DMT, N-demethylta- moxifen; RBA, relative binding affinity; ER, estrogen receptor. stock cultures (28) were inoculated into 25-sq cm flasks (Coming, N. Y.) Received April 15, 1983; accepted July 13, 1983. in 5 ml medium containing 5% fetal calf serum. When cell numbers 4618 CANCER RESEARCH VOL. 43 Downloaded from cancerres.aacrjournals.org on October 2, 2021. © 1983 American Association for Cancer Research. Tamoxifen Metabolites in MCF-7 Cells X1Ö5- 5X106- K>6- 5XW5- 1 10=- 3" 5X104- 10 8 104- 103- 103- 30 96 144 96 144 HOURS HOURS 5X10 10' 30 100 500 2500 5.000 10000 HOURS CONCENTRATION - nM Chart 1. Effect of tamoxifen (A),DMT (B), and 40HT (C)on the growth of MCF-7 cells. After 30 hr of exponential growth, cells were treated with tamoxifen, DMT, or 4OHT at concentrations of 0 (•).0.01(O), 0.1 (A), 0.5 (A), 2.5 (•),5(D), 7.5 (»),or10 ^M (O). Treated medium was changed daily thereafter, and cells were harvested and counted at 96 and 144 hr. D, cell counts at 144 hr for tamoxifen (•),DMT(A), and 4OHT (O).Points, mean of triplicate flasks from 2 experiments; bars, S.E. (n - 6). Inset, 2 to 10 nM4OHT compared with 1 pMtamoxifen at 120 hr; columns, mean of quadruplicate flasks; oars, S.E. reached approximately 1 x 10'yflask, the medium was replaced with supplied by I. C. I., Ltd., Pharmaceuticals Division, and frans-4-|3H|- fresh medium containing antiestrogen with or without 17/3-estradiol. The hydroxytamoxifen was prepared from this material by a modification of experimental medium was changed daily thereafter. Cells were harvested the high-performance liquid chromatography method of Foster ef al. (10) with 0.05% trypsin:0.02% EDTA (Flow Laboratories, Ryde, New South as follows. Isotope was applied to a Browntee RP-18 reverse-phase 10- Wales, Australia), and viable cells were counted under phase-contrast fim (22- x 0.7-cm) column and eluted in 75% methanol:25% water:0.1% on a hemocytometer or in a Model ZBI Coulter Counter (Coulter Elec diethylamine at 2.0 ml/min using a Waters Associates M45 solvent tronics, Hertfordshire, United Kingdom) after 2 and/or 4 doubling times delivery system. Column eluent was monitored by absorbance at 254 of the control population. nm and by radioactivity. The retention time of the c/s isomer was 24% Flow Cytometry. Harvested cells were stained for DMA flow cytometry longer than the frans isomer. The radioactive peak corresponding to as previously described (31) and analyzed on an ICP22 pulse cytometer /rans-4-hydroxytamoxifen was collected, dried under nitrogen, and redis- (Ortho Instruments, Westwood, Mass.). Estimates of the proportions of solved in ethanol. Aqueous solutions of fra/is-4-[3H]hydroxytamoxifen cells in Go-Gi, S, and G?-M phases of the cell cycle were computed from were prepared by drying a portion of the ethanolic solution under nitrogen the resulting DMA histograms (21). and redissolving in 10 mM Tris: 1.5 HIM EDTA buffer, pH 7.4 (TrisrEDTA Isotopes. [3H]Estradiol (100 Ci/mmol) was purchased from Amersham buffer) containing 0.2% bovine serum albumin. These solutions were International, Amersham, Buckinghamshire, United Kingdom, and [3H]- used within 24 hr of preparation. tamoxifen (71 Ci/mmol) from New England Nuclear, Boston, Mass. [3HJ- Determination of Binding Parameters. The cells used for binding 4OHT (42 Ci/mmol), a 1:1 mixture of the c/s and frans isomers, was studies were obtained by plating 2 x 106 logarithmically growing cells OCTOBER 1983 4619 Downloaded from cancerres.aacrjournals.org on October 2, 2021. © 1983 American Association for Cancer Research. R. R. Reddel et al. into 150-sq cm flasks in 50 ml medium and harvesting 6 to 7 days later nm ir §+ 1/1000 E2 m + 1/10E2 when cell numbers were 3 to 4 x 107 cells/flask.
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